Re: Fast string operations

Nicholas,

Thanks for the quick reply. Unfortunately I'm not using .NET 2.0 (yet!), so
I can't use Generics.

Would looping over chars like that slow things down significantly? Also, is
the char[] for each string cached with the string, or is a new one created
when you call things like ToCharArray() or foreach() on the string (not
every loop iteration, but on the first iteration)? Wouldn't I just be
replacing a new string instance with a new char[] and not get any net gain
over just calling .Trim()?

In your opinion, if I weren't against unsafe code, could I make this
significantly faster, or would it not afford me much difference?

As far as performance, on some of our clients' instances, memory growth is
rapid. It seems the more memory they have, the faster it grows which leads
me to believe that the GC is being lax since it has so much free memory and
doesn't see the need to aggressively collect memory. But it bothers our
clients and they perceive this to be a memory leak.

I realize it's an education issue, but I want to make sure that I'm
educating them correctly, as opposed to just making up a B.S. excuse and
Jedi hand-waving about the GC stuff.

Also, it's not an ASP.NET application, it's an ASP app that used to call
into VB6 COM objects. We've replaced the VB6 objects with .NET objects
exposing a "compatibility layer" that has a ComVisible API that is identical
(though not binary compatible) with the old VB6 stuff. Late-bound clients
don't know the difference other than a different ProgID for the COM objects.

So we're dealing with the wkst GC, as far as I know (since only ASP.NET uses
svr unless you host the CLR yourself, from what I understand). I'm not sure
how I'd even do that in an ASP/COM-interop situation, but, assuming it's
possible, would writing our own CLR host to use the svr GC help matters at
all?

Most of our clients' servers are dual-or-more processor boxes.

Thanks again,
Chad Myers

"Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
message news:Ozam7ZuZFHA.580@xxxxxxxxxxxxxxxxxxxxxxx
> Chad,
>
> For the first scenario, your solution should give you an increase.
>
> For the second scenario, you should use reflection once to get a
> reference to the internal static character array WhitespaceChars on the
> string class. Then, you can write a method which will cycle through a
> string passed to it, like so:
>
> public static bool TrimIsNullOrEmpty(string value)
> {
> // If null, then get out.
> if (value == null)
> {
> // Return true.
> return true;
> }
>
> // Cycle through the characters in the string. If the character is not
> found
> // in the whitespace array, return false, otherwise, when done, return
> true.
> foreach (char c in value)
> {
> // If the character is not found in the WhitespaceArray, then
> return
> // false.
> if (Array.IndexOf<char>(WhitespaceArray, char) == -1)
> {
> // Return false.
> return false;
> }
> }
>
> // Return true, the string is full of whitespace.
> return true;
> }
>
> I used the generic version of the IndexOf method on the Array class in
> order to eliminate boxing. Also, if you really want to squeeze out every
> last bit of performance from this, you can take the WhitespaceArray and
> use the characters as keys in a dictionary. The number of whitespace
> characters is 25 (right now, that is). However, if your strings typically
> are padded with spaces, then you could get a big speed boost by copying
> the array initially, and then placing the space character as the first
> element in the array (which would cause most of the calls to IndexOf to
> return very quickly, probably quicker than a lookup in a dictionary).
>
> I am curious though, are you seeing a performance issue, or do you just
> see the numbers and are worried about them? ASP.NET applications tend to
> get in a nice groove with the GC over time.
>
> Hope this helps.
>
> --
> - Nicholas Paldino [.NET/C# MVP]
> - mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> "Chad Myers" <cmyers@xxxxxxxxxxxxxxxxxxxxx> wrote in message
> news:2rone.13780$PR6.9706@xxxxxxxxxxxxxxxxxxxxxxx
>> I've been perf testing an application of mine and I've noticed that there
>> are a lot (and I mean A LOT -- megabytes and megabytes of 'em)
>> System.String instances being created.
>>
>> I've done some analysis and I'm led to believe (but can't yet
>> quantitatively establish as fact) that the two basic culprits are a lot
>> of calls to:
>>
>> 1.) if( someString.ToLower() == "somestring" )
>>
>> and
>>
>> 2.) if( someString != null && someString.Trim().Length > 0 )
>>
>>
>> ToLower() generates a new string instance as does Trim().
>>
>> I believe that these are getting called many times and churning up a
>> bunch of strings faster than the GC can collect them, or perhaps there's
>> some weird interning/caching thing going on. Regardless, the number of
>> string instances grows and grows. It gets bumped down occasionally, but
>> it's basically 5 steps forward, 1 back.
>>
>> For reference, this is an ASP application calling into .NET ComVisible
>> objects. So I assume this uses the workstation GC, right?
>>
>>
>> Anyhow, so I think that I can solve problem (1) with String.Compare()
>> which can perform in-place case-insensitive comparisons without
>> generating new string instances.
>>
>> Problem (2), however, is more complicated. There doesn't appear to be a
>> TrimmedLength or any type of method or property that can give me the
>> length of a string, minus whitespace and without generating a new string
>> instance, in the BCL.
>>
>> I suppose I could do some unsafe, or even unmanaged code (which is what
>> MSFT did for all their string handling stuff inside System.String and
>> using the COMString stuff), but I'd like to try to avoid that, or at
>> least use a library that's already written and well tested.
>>
>> Any thoughts?
>>
>> Thanks in advance,
>> Chad Myers
>>
>>
>
>


.

Relevant Pages

  • Re: Deadlock in Solaris 8
    ... Are you using stl strings? ... operator created a new string instance from the constant data. ... which killing performance due to the multiprocessor environment. ...
    (comp.unix.solaris)
  • Re: System.String: It doesnt seem to act like a reference type.
    ... First, because Strings are immutable, changing the value of a string ... doesn't really change the string _in situ_ in memory. ... creates a whole new string and points the String reference to it. ... the new String instance instead of the old ...
    (microsoft.public.dotnet.languages.csharp)
  • Re: Fast string operations
    ... Regardless, even with your suggestion, the .Trim() still creates a new ... > My assumption here is that you already intend to trim the string before it ... >> ToLowergenerates a new string instance as does Trim. ...
    (microsoft.public.dotnet.languages.csharp)
  • Re: Trimming whitespaces
    ... > have a bit of c code that is ment to take a string (that may or ... > and trims off the whitespace before and after. ... char *trim ...
    (comp.lang.c)
  • Re: Strings odd one out
    ... > My understanding of classes is that a class serves as a wrapper for ... or they can be called by a literal String. ... A Java String ... just like any other String instance when the program runs. ...
    (comp.lang.java.programmer)